[Growth of the hoof horn in horses with chronic laminitis]

Abstract

Objective of the study was to investigate whether a correlation between rotation and/or sinking of the third phalanx (P3) and changes of horn growth on the hoof wall exists.

Material and methods: In 117 hooves of euthanatized or slaughtered horses with chronic laminitis the rotating angle to palmar/plantar and medial/lateral and a sinking of P3 were assessed on radiographs. Defined distances were measured on the dorsal hoof wall as well as in the heel to assess the horn growth of a hoof. On the basis of saw cuts of the hooves, the course of the horn tubes was judged.

Results: A rotation angle of approximately 8° was found to predict a change in the direction of the growth of the hoof horn at the dorsal and the lateral hoof wall. In addition, a correlation between the rotation angle of P3 and the length of growth of the hoof could be highlighted. A greater angle could lead to a larger interruption of the dorsal horn growth; meanwhile the palmar/plantar horn growth appeared to be independent. A correlation between a medial/lateral rotation of the pedal bone and the length of the horn was not observed.

Conclusion: The direction change of the horn tubes might cause a decrease of the visible length growth of a chronic laminitic hoof. Therefore, it appears to be important to differentiate between the externally visible length of the hoof and the real growth of the horn. Apparently, the amount of horn produced is the same on the dorsal hoof wall and in the heel. In horses with moderate laminitis the horn tubes on the dorsal wall were lying in folds, with the consequence of a decreased visible length growth. Only the formation of wrinkles of the horn tubes on the dorsal hoof wall reduced the visible wall length. Formation of wrinkles of the horn tubes in the heel could not be observed. Interestingly, the results of this study show that the lateral rotation of P3 does not promote the formation of wrinkles of the horn tubes along the lateral or medial hoof wall.

Clinical relevance: According to our results, a resection of the dorsal hoof wall might be a sensible therapeutic approach in horses with chronic laminitis showing a rotation of P3 of at least 8°.